Method and structure for testing and calibrating three axis magnetic field sensing devices

Abstract

A structure and method are provided for self-test of a Z axis sensor. Two self-test current lines are symmetrically positioned adjacent, but equidistant from, each sense element. The vertical component of the magnetic field created from a current in the self-test lines is additive in a flux guide positioned adjacent, and orthogonal to, the sense element; however, the components of the magnetic fields in the plane of the sense element created by each of the two self-test current line pairs cancel one another at the sense element center, resulting in only the Z axis magnetic field being sensed during the self-test.

What is claimed is: 
     
       1. A magnetic field sensor comprising:
 a substrate having a surface; 
 a first magnetoresistive sensor comprising:
 a first sensing element having a first side lying parallel to the surface of the substrate, and a second side opposed to the first side and having first and second opposed edges; and 
 a first flux guide disposed adjacent to the first side of the sensing element and having an end that is proximate to the first edge and the first side of the sensing element, 
 wherein the first sensing element defines a first long axis and a first plane through the first long axis, the first plane being perpendicular to the surface; 
 
 a second magnetoresistive sensor comprising:
 a second sensing element having a first side lying parallel to the surface of the substrate, the second sensing element having a second side opposed to the first side and having first and second opposed edges; and 
 a second flux guide disposed adjacent to the first side of the second sensing element and having an end that is proximate to the second edge and the first side of the second sensing element, 
 wherein the second sensing element defines a second long axis and a second plane through the second long axis, the second plane being perpendicular to the surface; 
 
 a third magnetoresistive sensor comprising:
 a third sensing element having a first side lying parallel to the surface of the substrate, the third sensing element having a second side opposed to the first side and having first and second opposed edges; and 
 a third flux guide disposed adjacent to the first side of the third sensing element and having an end that is proximate to the second edge and the first side of the third sensing element; and 
 
 a fourth magnetoresistive sensor comprising:
 a fourth sensing element having a first side lying parallel to the surface of the substrate, the fourth sensing element having a second side opposed to the first side and having first and second opposed edges; and 
 a fourth flux guide disposed adjacent to the first side of the fourth sensing element and having an end that is proximate to the first edge and the first side of the fourth sensing element; 
 
 a first pair of self-test current carrying lines, the first pair of self-test current carrying lines including a first and a second self-test current carrying line disposed parallel to the second side of the first sensing element and spaced away from the first and second edges of the first sensing element, the first and second self-test current carrying lines being equidistant from, parallel to, and on opposed sides of the first plane and configured to create a magnetic field that is orthogonal to a sensor plane of the first, second, third, and fourth magnetoresistive sensors, wherein a first component of a first magnetic field in a third plane that is parallel to the surface and created by a first current in a first direction in the first self-test current carrying line, and a second component of a second magnetic field in the third plane and created by a second current in a second direction in the second self-test current carrying line cancel one another at the intersection of the first plane and the first long axis of the sensing element, and components of the first and second magnetic fields that are parallel to the first plane are additive at the first flux guide and a portion of the components of the first and second magnetic fields that are parallel to the first plane are guided into the sensing element as a third component, wherein the first and second self-test current carrying lines are disposed parallel to the second side of the third sensing element and spaced away from the first and second edges of the third sensing element; and 
 a second pair of self-test current carrying lines disposed parallel to the second side of the second sensing element and spaced away from the first and second edges of the second sensing element, each self-test current carrying line of the second pair being equidistant from, parallel to, and on opposed sides of the second plane and configured to create a magnetic field that is orthogonal to the sensor plane of the first, second, third, and fourth magnetoresistive sensors, wherein the second pair of self-test current carrying lines are disposed parallel to the second side of the fourth sensing element and spaced away from the first and second edges of the fourth sensing element, 
 wherein the first, second, third, and fourth magnetoresistive sensors are coupled in a Wheatstone bridge configuration, the first and second magnetoresistive sensors are connected in parallel, the first and third magnetoresistive sensors are coupled in series, and the second and fourth magnetoresistive sensors are coupled in series. 
 
     
     
       2. The magnetic field sensor of  claim 1 , wherein the third component comprises a magnitude that is proportional to the size and shape of the first flux guide and inversely proportional to the distance between the first flux guide and the first sensing element. 
     
     
       3. The magnetic field sensor of  claim 1 , wherein the first flux guide comprises a high permeability material. 
     
     
       4. The magnetic field sensor of  claim 1 , comprising a stabilization line perpendicular to the first pair of self-test current carrying lines and adjacent the first magnetoresistive sensor. 
     
     
       5. A magnetic field sensor comprising:
 a substrate having a planar surface; and 
 a first bridge circuit comprising a first magnetoresistive sensor, a second magnetoresistive sensor, a third magnetoresistive sensor, and a fourth magnetoresistive sensor coupled as a Wheatstone bridge for sensing a magnetic field in a first direction that is orthogonal to a plane of the first, second, third, and fourth magnetoresistive sensors; 
 the first magnetoresistive sensor comprising:
 a first sensing element having a first side lying parallel to the planar surface of the substrate, the first sensing element having a second side opposed to the first side and having first and second opposed edges; and 
 a first flux guide disposed orthogonal to and spaced from the first edge of the first sensing element; 
 
 the second magnetoresistive sensor comprising:
 a second sensing element having a first side lying parallel to the planar surface of the substrate, the second sensing element having a second side opposed to the first side and having first and second opposed edges; and 
 a second flux guide disposed orthogonal to and spaced from the second edge of the second sensing element; 
 
 the third magnetoresistive sensor comprising:
 a third sensing element having a first side lying parallel to the planar surface of the substrate, the third sensing element having a second side opposed to the first side and having first and second opposed edges; and 
 a third flux guide disposed orthogonal to and spaced from the second edge of the third sensing element; and 
 
 the fourth magnetoresistive sensor comprising:
 a fourth sensing element having a first side lying parallel to the planar surface of the substrate, the fourth sensing element having a second side opposed to the first side and having first and second opposed edges; and 
 a fourth flux guide disposed orthogonal to and spaced from the first edge of the fourth sensing element, 
 wherein the first, second, third, and fourth, sensing elements define a first plane, and 
 
 wherein the first bridge circuit further comprises: 
 a first self-test current carrying line and a second self-test current carrying line disposed parallel to the second side of the first and third sensing elements and spaced away from the first and second edges of the first and third sensing elements, the first and second self-test current carrying lines being equidistant from, parallel to, and on opposed sides of a second plane perpendicular to the first plane and configured to create a magnetic field that is orthogonal to the plane of the first, second, third, and fourth magnetoresistive sensors of the first bridge circuit; 
 a third self-test current carrying line and a fourth self-test current carrying line disposed parallel to the second side of the second and fourth sensing elements and spaced away from the first and second edges of the second and fourth sensing elements, the third and fourth self-test current carrying lines being equidistant from, parallel to, and on opposed sides of a third plane perpendicular to the first plane, and configured to create a magnetic field that is orthogonal to the plane of the first, second, third, and fourth magnetoresistive sensors of the first bridge circuit. 
 
     
     
       6. The magnetic field sensor of  claim 5 , wherein a first component of a first magnetic field in a fourth plane parallel to the planar surface and created by a first current in a first direction in the first self-test current carrying line, and a second component of a second magnetic field in the fourth plane and created by a second current in a second direction in the second self-test current carrying line cancel one another at the intersection of the second plane and a first long axis of the first and third sensing elements, and the first and second magnetic field components parallel to the second plane are additive at the first and third flux guides, and a portion of components orthogonal to the plane of the first, second, third, and fourth magnetoresistive sensors of the first bridge circuit are guided into the first and third sensing elements as a third component. 
     
     
       7. The magnetic field sensor of  claim 6 , wherein the third component comprises a magnitude that is proportional to a size and a shape of the first flux guide and inversely proportional to a distance between the first flux guide and the first sensing element. 
     
     
       8. The magnetic field sensor of  claim 5 , wherein at least one of the first, second, and third flux guides includes a high permeability magnetic material. 
     
     
       9. The magnetic field sensor of  claim 8 , wherein the high permeability magnetic material of the at least one of the first, second, and third flux guides includes a soft ferromagnetic material. 
     
     
       10. The magnetic field sensor of  claim 8 , wherein the high permeability magnetic material includes nickel iron. 
     
     
       11. The magnetic field sensor of  claim 5 , wherein one or more of the first, second, third, and fourth flux guides is disposed below the first, second, third, and fourth sensing elements, respectively. 
     
     
       12. The magnetic field sensor of  claim 5 , further comprising:
 a first stabilization line perpendicular to the first, second, third, and fourth self-test current carrying lines and adjacent the first and second sensing elements. 
 
     
     
       13. The magnetic field sensor of  claim 12 , further comprising:
 a second stabilization line perpendicular to the first, second, third, and fourth self-test current carrying lines and adjacent the third and fourth sensing elements.